Articles comprising a polyolefin-based element joined to a polyamide-based element, and process for obtaining them

ABSTRACT

The invention concerns manufactured articles comprising at least two assembled thermoplastic elements, a first element based on polyolefin and a second element based on polyamide. The elements are assembled by being welded together.

The present invention relates to manufactured articles comprising atleast two elements made of thermoplastics which are joined together,namely a first element based on a polyolefin and a second element basedon a polyamide. These articles are particularly useful in the automobileand sports equipment sectors.

The choice of a thermoplastic for producing manufactured articles formedfrom the latter is generally guided by criteria based on costs andproperties. Thus, depending on the use to which an article will be putand the environment in which it will be used, different properties willbe required, such as toughness, stiffness, flexibility, dimensionalstability, deflection temperature under load, thermal withstand,impermeability to certain chemicals, resistance to contact with certainsubstances, etc.

Among the materials used, thermoplastic polyolefins generally have a lowcost. As examples, mention may be made of polyethylene andpolypropylene.

Polyamides have a higher level of performance. For example, they exhibitbetter mechanical behavior at high temperatures.

To find the best cost/properties comprise, it is known to producearticles by assembling elements formed from different materials. Suchassemblies make it possible to use the most suitable material for eachfunctional part of the article.

The operation of assembling the various elements must also be taken intoaccount in the design of an article: it may incur additional costs andhave an impact on the characteristics of the article (degradation of themechanical properties, creation of an area of weakness, poor sealing,etc.). The mode of assembly may therefore be an essential characteristicfor the production of manufactured articles.

To produce assemblies of polyolefin and polyamide elements, it is knownto use mechanical means. For example, it is known to assemblerespectively polyamide and polyethylene tubular parts by means of asleeve into which the elements are screwed or fitted. The mechanicalassembly operation may result in sealing defects and may in certaincases prove to be ill-suited.

It is also known to adhesively bond the elements. This mode of assemblyrequires the application of a layer of adhesive, sometimes in areas thatare difficult to reach. This may in certain cases be a drawback andentail an additional cost.

Polyamides and polyolefins are chemically incompatible materials, thatis to say they cannot be blended together. This incompatibility preventsthem from being welded to each other.

The subject of the present invention is articles comprising respectivelypolyamide-based and polyolefin-based elements, exhibiting anotherstructure, especially another assembly. The articles according to theinvention exhibit excellent mechanical properties and provide excellentsealing at the point of assembly.

For this purpose, the invention proposes an article comprising at leasttwo elements made of thermoplastics which are joined together, a firstelement being formed from a material based on a polyolefin and a secondelement being formed from a material comprising a polyamide,characterized in that the material of the second element is acomposition comprising at least one polyamide and a compatibilizer forpolyamides and polyolefins, and in that the assembly operation iscarried out by welding the two elements together over at least a portionof the surfaces of the latter.

The expression “assembly of elements” is understood to mean anystructure in which at least two elements are brought into contact witheach other over at least a portion of their respective surfaces and areconsolidated at the contact surface. According to the invention,consolidation is obtained by welding.

The two elements may be brought into contact with each other over planeportions of their surfaces, or over curved portions. Preferably, thesurfaces brought into contact with each other cooperate to form acontinuous weld line or a continuous weld area.

According to one particular embodiment of the invention, those portionsof the elements brought into contact with each other are of conjugateshapes. For example, they may be socketed. As an example, a tubularportion of one element may be inserted into a tubular portion of theother element, having a slightly larger diameter.

The polyolefin used for producing the first element is preferably chosenfrom polyethylenes, polypropylenes and copolymers based on ethylene andα-olefins. As examples, mention may be made of polyethylenes,polyethylene, low-density polyethylenes and high-density polyethylenes.

The compatibilizer used for implementing the invention is preferablychosen from the family of ionomers. Ionomers are ionic copolymers havingrepeat units of at least one α-olefin and at least one unsaturated α,β-carboxylic acid, at least some of the acid units of which are ionizedwith a metal ion. The α-olefin preferably contains 2 to 6 carbon atomsand the acid preferably contains 3 to 6 carbon atoms. The α-olefin ispreferably ethylene and the acid is preferably acrylic or methacrylicacid. Other monomers may be used in a complementary manner, such asacrylates or methacrylates. The metal ion may be monovalent, divalent ortrivalent, such as for example sodium, zinc, aluminum and potassiumions. As an example of an ionomer that can be used, mention may be madeof the (80/10/10) ethylene/isobutyl acrylate/methacrylic acid copolymer70% neutralized with zinc.

Ionomers that can be used for implementing the invention are those soldunder the name SURLYN® by DuPont de Nemours.

The composition from which the second element is formed preferablycontains, in addition to the polyamide and the compatibilizer, apolyolefinic compound. The term “polyolefinic compound” is understood tomean a compound of polymeric type which comprises olefinic repeat units.This may, for example, be a thermoplastic or an elastomer.

According to a first embodiment of the invention, the polyolefiniccompound is a thermoplastic, preferably of the same kind as that fromwhich, or on the basis of which, the first element is formed. Thepolyolefin is preferably chosen from polyethylenes and polypropylenes.In addition, it may be functionalized, for example by maleic anhydride.It may also be advantageous to use a blend of a functionalizedpolyethylene and a nonfunctionalized polyethylene.

According to another embodiment of the invention, the polyolefiniccompound is elastomeric in character. As examples, mention may be madeof ethylene-propylene rubbers (EPR) and ethylene-propylene-diene monomerrubbers (EPDM). Optionally, these compounds may be functionalized bymaleic anhydride.

The polyamide included in the composition forming the material of thesecond element is preferably chosen from semicrystalline polyamides, forexample polymers obtained by a polycondensation reaction of saturatedaliphatic dicarboxylic acids having from 6 to 12 carbon atoms, such asfor example adipic acid, azelaic acid, sebacic acid, dodecanoic acid ora mixture thereof, with diprimary diamines, preferably linear orbranched saturated aliphatics having from 4 to 12 carbon atoms, such as,for example, hexamethylenediamine, trimethylhexamethylenediamine,tetramethylenediamine, m-xylenediamine or a mixture thereof; polyamidesobtained either by direct homopolycondensation of an ω-aminoalkanoicacid comprising a hydrocarbon chain having from 4 to 12 carbon atoms, orby hydrolytic opening and polymerization of lactams derived from theseacids; copolyamides obtained from the starting monomers for theaforementioned polyamides, it being possible for the acid component ofthese copolyamides to furthermore consist partly of terephthalic acidand/or isophthalic acid; and blends of these polyamides or theircopolymers.

By way of illustration of the polyamides obtained by thepolycondensation of diacides and diamines, mention may be made, forexample, of:

nylon-4,6 (a polymer obtained from tetramethylenediamine and adipicacid);

nylon-6,6 (a polymer obtained from hexamethylenediamine and adipicacid);

nylon-6,9 (a polymer obtained from hexamethylenediamine and azelaicacid);

nylon-6,10 (a polymer obtained from hexamethylenediamine and sebacicacid);

nylon-6,12 (a polymer obtained from hexamethylenediamine anddodecanedioic acid).

As an illustration of the polyamides obtained by homopolycondensationthat may be suitable, mention may be made of:

nylon-4 (a polymer obtained from 4-aminobutanoic acid or fromγ-butyrolactam);

nylon-5 (a polymer obtained from 5-aminopentanoic acid or fromδ-amylolactam);

nylon-6 (a polymer obtained from ε-caprolactam);

nylon-7 (a polymer obtained from 7-aminoheptanoic acid);

nylon-8 (a polymer obtained from capryllactam);

nylon-9 (a polymer obtained from 9-aminononanoic acid);

nylon-10 (a polymer obtained from 10-aminodecanoic acid);

nylon-11 (a polymer obtained from 11-aminoundecanoic acid);

nylon-12 (a polymer obtained from 12-aminododecanoic acid or fromlaurylactam).

By way of illustration of copolyamides, mention will be made, forexample, of:

nylon-6,6/6,10 (a copolymer obtained from hexamethylenediamine, adipicacid and sebacic acid);

nylon-6,6/6 (a copolymer obtained from hexamethylenediamine, adipic acidand caprolactam);

nylon-6/12;

nylon-6/11;

nylon-6/6,36.

The preferred polyamides of the invention are nylon-6,6 polyamides,nylon-6 polyamides and nylon-6,6/6 and nylon-6/6,36 copolyamides.

The thermoplastics from which the elements are formed may advantageouslyinclude fillers, for example reinforcing fillers, such as glass fibers,fibers made of thermosetting synthetic materials or materials having amelting point above 325° C., carbon fibers, and/or mineral powders suchas talc, mica, kaolin and calcium carbonate. These fillers are widelyused in the fields of plastics technology.

They may also include additives usually added to thermoplasticcompositions, such as stabilizers, plasticizers, fire retardants,antioxidants, lubricants or other conventional additives.

Any known process may be used to produce elements formed from athermoplastic comprising several components. For example, mention may bemade of:

forming from granules of a composition containing all the elements;

forming from blends of granules of different compositions and optionallyof additives introduced in powder or masterbatch form, for examplegranules of polyethylene, polyamide and ionomer;

forming from granules, some of which are coated with an additive oranother compound.

The compositions comprising a polyamide, a compatibilizer and apolyolefinic compound generally have a continuous phase and a dispersedphase within the continuous phase. The nature of the components andtheir concentration are advantageously chosen so that the continuousphase consists of a polyamide and the dispersed phase consists of thepolyolefinic compound. This morphology may allow the material to havethe characteristic properties of the polyamide. It may allow, forexample, the permeability to fuels to be maintained at a sufficientlylow level. The composition of which the second element is madepreferably exhibits good impermeability to fuels containing alcohols.

The two elements may be formed using conventional processes, among whichmention may be made of injection molding, extrusion blow molding, gasinjection molding and water injection molding. The elements may possiblyhave a cavity or a hollow portion.

According to one particular embodiment, the two elements are hollow orhave a hollow cross section and are assembled so that the hollowportions of each of the elements communicate with each other. Theassembly is advantageously produced by shape complementarity.

The second element may, for example, be a tubular conduit.

To produce a second element of tubular shape, the technique of extrusionblow molding may be preferred. For this purpose, the polyamide-basedcomposition preferably has a melt flow index of between 0.5 g/10 min and8 g/10 min, determined by applying a load of 5 kg at 275° C. Inaddition, it may advantageously have a modulus of less than 1500 MPa,preferably less than 1000 MPa, which gives the element a sufficientdegree of flexibility, which may make it easier to mount the articlesand avoid forming them with a complex profile. The second element mayalso have bellows portions allowing its flexibility to be furtherimproved. According to another beneficial feature, the composition mayhave a notched Izod impact strength, measured at 23° C., of greater than800 J/m.

The final consolidation of the parts after assembly is carried out bywelding. After the surfaces have been brought into contact with eachother, they are, for example, raised to a temperature at least above thesoftening point of the materials constituting the elements, preferablyclose to the melting point.

As known welding techniques suitable for the invention, mention may bemade, for example, of:

ultrasonic welding: the surfaces are heated to the desired temperatureby ultrasound; vibration welding: the surfaces are brought into contactand vibrating one with respect to the other, the friction between thesurfaces causing the material to heat up and soften; hot-plate welding:a heated plate is placed between the welding surfaces and then removedwhen these have reached the desired temperature. The surfaces are thenbrought into contact with each other under a defined pressure; infraredwelding: a technique similar to that of hot-plate welding, laserwelding. the heat source emitting infrared radiation;

Further details and advantages of the invention will become more clearlyapparent in the light of the examples given below solely by way ofindication.

EXAMPLES

The following compositions were produced:

Composition 1

Composition obtained by extruding a blend consisting of 20% by weight ofgranules of an ionomer sold by DuPont under the name SURLYN® 1652 and80% by weight of the following elastomerized polyamide composition:

57.4% by weight of a nylon-6 polyamide sold by Rhodia EngineeringPlastics under the reference TECHNYL C 502, having a relative viscosityof 5;

40% by weight of a maleic anhydride-grafted ethylene-propylene elastomersold by Exxon under the name EXXELOR VA 1801;

2.6% of pigments and lubricants (carbon black and calcium stearate).

Composition 2:

Composition obtained by extruding:

57.4% by weight of a nylon-6 polyamide sold by Rhodia EngineeringPlastics under the reference TECHNYL C 502, having a relative viscosityof 5;

30% of a high-density polyethylene (HDPE) sold by BASF under the nameLUPONEN ELENAC;

10% of an ionomer sold by DuPont under the name SURLYN® 1652;

2.6% of pigments and lubricants (carbon black and calcium stearate).

Plaques were formed by injection molding, using composition 1.composition 2, the elastomerized polyamide described above, and thehigh-density polyethylene described above.

The plaques were welded together in pairs, holding them for about 10seconds at 320° C. using the hot-plate welding technique. The force innewtons needed to separate the two plaques was measured. It is given inTable I.

TABLE I Elastomerized PA-6 HDPE (comparative example) (element 1)Composition 1 650 780 (element 2) Composition 2 940 840 (element 2)Elastomerized PA-6 1000 0 (element 2, comparative example)

Compositions 1 and 2 have a greater ability to be welded to polyethylenethan that of a polyamide not according to the invention.

The permeability to fuels of compositions 1 and 2, of the elastomerizedpolyamide and of the high-density polyethylene were measured.

The permeability of the tubes manufactured was evaluated using a staticmethod. A tube specimen 300 mm in length was closed at one of its endswith a nylon plug covered with a fuel-resistant adhesive. The tube wasconnected at its other end to a fuel tank with a capacity of 25 cm³, inorder thereby to keep the composition of the fuel in the tube constant.The tube was conditioned in terms of temperature and of fluidimpregnation in order thus to obtain a direct measurement of thepermeability. The tests were carried out at 40° C. and the diffusion wasdetermined by the weight loss over a defined period, for example afterperiods of 24 hours.

Thus, the permeability corresponds to the rate of weight loss of thespecimen determined when the weight loss for successive periods isconstant.

The measurements (in g/m².day) are given in Table II for various fuels.

TABLE II Diesel fuel Fuel without containing 22% Fuel containing alcoholalcohol 6.5% alcohol Elastomerized 0 11 26 PA-6 HDPE 40 38 54Composition 1 0 0 0 Composition 2 0 0 11

These results show that the compositions exhibit excellentimpermeability to the fuels.

1. A process for manufacturing articles by forming elements made of athermoplastic and then joining them together, wherein the joiningoperation is carried out by bringing the elements into contact with eachother over at least a portion of their surfaces and then welding the twoelements over at least a portion where the two elements are in contact,at a temperature above the softening point of the materials constitutingthe elements, a first element being formed from a material based on apolyolefin and a second element being formed from a material comprisinga polyamide, wherein the material of the second element is a compositioncomprising at least one polyamide and a compatibilizer for polyamidesand polyolefins.
 2. The process as claimed in claim 1, wherein thewelding is carried out by means of a laser.
 3. The process as claimed inclaim 1, wherein the welding is carried out by a vibration weldingtechnique.
 4. The process as claimed in claim 1, wherein the welding iscarried out by an ultrasonic welding technique.
 5. The process asclaimed in claim 1, wherein the welding is carried out by a hot-platewelding technique.
 6. The process as claimed in claim 1, wherein thewelding is carried out by an infrared welding technique.
 7. The processas claimed in claim 1, wherein the compatibilizer is an ionomer.
 8. Theprocess as claimed in claim 1, wherein the material of the secondelement is a composition comprising a polyamide, an ionomer and apolyolefinic compound.
 9. The process as claimed in claim 8, wherein thepolyolefinic compound is an elastomer or a thermoplastic.
 10. Theprocess as claimed in claim 8, wherein the polyolefinic compound is athermoplastic of the same kind as that from which the first element isproduced.
 11. The process as claimed in claim 1, wherein the polyamideis selected from the group consisting of nylon-6, nylon-11, nylon-12,nylon-4,6, nylon-6,10, nylon-6,6, nylon-6,10, nylon-6,36, copolymers andblends based on these polymers.
 12. The process as claimed in claim 1,wherein the composition has a melt flow index of between 0.5 g/10 minand 8 g/10 min, measured under a load of 5 kg at a temperature of 275°C.
 13. The process as claimed in claim 1, wherein the polyolefin isselected from the group consisting of polyethylenes, polypropylenes,copolymers and blends based on these polymers.
 14. The process asclaimed in claim 8, wherein the polyolefinic compound is polyethylene.15. The process as claimed in claim 8, wherein the polyolefinic compoundis an ethylene-propylene rubber functionalized by maleic anhydride. 16.The process as claimed in claim 8, wherein the composition has acontinuous phase and a dispersed phase within the continuous phase, thecontinuous phase comprising the polyamide and the dispersed phasecomprising the polyolefinic compound.
 17. The process as claimed inclaim 1, wherein the elements are obtained by using a technique selectedfrom the group consisting of injection molding, extrusion blow molding,gas injection molding and water injection molding.
 18. The process asclaimed in claim 1, wherein the two elements are hollow, assembled bythe complementarity of the shapes so that the hollow portions of each ofthe elements communicate with each other.
 19. The process as claimed inclaim 18, wherein the second element is a tubular conduit.